What is the meaning of angle brackets in Python?

Question

I found the following lines in the scikit-learn package:

if is_sparse:
    problem = csr_set_problem(
            (

        

Answer 1

That is Cython's syntax for type casting/coercion. It is not plain Python. Notice the file extension is .pyx

You can learn more about them in the documentation for Cython.

Here's an example taken from the doc page:

cdef char *p, float *q
p = q

Using Cython is not uncommon with projects like scikit-learn, where one gains significant optimisations by mixing readable Python with blazing-speed C.